The invention relates to a semiconductor device with a semiconductor body comprising a layer-shaped region of a first conductivity type which adjoins a surface and which is provided with a high-voltage MOST which comprises a source zone of the second, opposed conductivity type adjoining the surface and a drain zone of the second conductivity type adjoining the surface and separated from the source zone by an interposed channel region, which drain zone comprises a strongly doped surface zone situated at a distance from the channel region and a weakly doped zone which forms a drain extension, is connected to the former zone, and extends up to the channel region, said source and drain zones of the transistor having an interdigitated configuration with at least three elongate zones of the second conductivity type lying next to one another, of which the central zone forms part of the drain zone and comprises at least an end face, while the two outermost zones situated on either side of the central zone each form part of the source zone.
MOS transistors with interdigitated source/drain configurations are generally known. It is possible to obtain a current-passing capacity or an ON-resistance which are sufficiently high or sufficiently low for the specific function of the transistor through the number of fingers and/or the length of the fingers. It is usual to provide the source zone and the channel region not only along the longitudinal sides of the drain fingers but also around the end faces of the drain fingers so as to achieve a maximum efficiency in space utilization in the semiconductor body. It is generally known, furthermore, that the breakdown voltage of a field effect transistor can be increased in that the drain is provided with a high-ohmic drain extension situated between the low-ohmic drain and the channel region.
It was found in practice that the current-voltage area within which a MOS transistor of the kind indicated above can be safely operated (SOAR=safe operating area) is often smaller than might be expected. It appears more in particular that the breakdown voltage of the transistor is strongly reduced at great current densities.